Radio frequency-based wireless monitoring of sleep apnoea patient

Abstract

Radio frequency (RF) technology plays a significant role in the development of portable devices. Well-designed RF circuits may reduce the dimensions of portable medical devices, which will provide a more comfortable monitoring environment and may lead to more accurate diagnosis. This research is focused on the use of RF technology to develop a wearable wireless multi-parameter human monitoring system suitable for sleep apnoea research. In this thesis, an innovative system prototype employing RF and microwave technology is proposed. The thesis focusses on research into specified passive and active microwave circuits, 5.8 GHz signal propagation and concept approval at the system level. Specially-designed microwave bandpass (BPF) and lowpass filters (LPF) are presented in the thesis. These filters are designed based on the required specifications for the system. The designed BPF uses a combination of compact microstrip resonant cell (CMRC) and defected ground structure (DGS) technologies, which is able to satisfy a narrow bandwidth of 60 MHz and a selectivity of 0.22 dB/MHz, as required in the system specification. The LPF designs also use CMRC and DGS technologies. The achieved LPFs have the characteristics of sharp roll-off, low insertion loss, compact size and wide stop-bandwidth. 2.4 GHz and 5.8 GHz circular patch antennas are designed for the proposed wireless on-body transducer system, and the 5.8 GHz signal penetration capability has been tested in a simulated monitoring environment. The results prove that the 5.8 GHz microwave signal can be applied in the wireless monitoring of sleep apnoea patients. In the active design section, the design principles of a Class AB power amplifier and Class E oscillator using GaN HEMT technology are introduced. The designed circuits are able to achieve an appropriate output power level with a high power-added efficiency. These designs can be applied in a wireless power transmission system. Therefore, the battery can be completely removed from the on-body transducer, leading to significant saving of space. The cost of the portable transducer device may also be reduced at the same time. The sleep apnoea wireless monitoring system consists of two building blocks: an RF-based wireless on-body transducer and remote base station. The on-body prototype has a microstrip circular patch antenna, a project-oriented microstrip BPF, a frequency mixing circuit, a modulation circuit and a differential circuit for biomedical signal detection. The development of the on-body prototype was divided into five stages. For each of the developmental stages, the prototype underwent the phases of design, modelling, simulation, fabrication and measurement. The testing results for each phase and stage are very promising. The proposed prototype has been tested from baseband to 2.4 GHz RF band with excellent results. The research will benefit both sleep apnoea patients and hospitals by reducing the cost of the device, and the reduced size of the portable wireless patient monitoring device will enable patients to be more comfortable during diagnosis. The research reported in this thesis has made significant contributions in the following fields: (1) the development of a novel design of microstrip filters using CMRC and DGS, (2) successful 5.8 GHz signal penetration capability in a simulated environment for sleep apnoea monitoring, (3) the development of a high efficiency and high output power amplifier and oscillator for wireless power transmission and (4) concept approval of the proposed novel wireless on-body transducer.